1. Field of the Invention
This invention relates to a protocol data generator-analyzer, and particularly relates to a protocol data generator-analyzer to encode and decode PDUs (Protocol Data Units) in control and management of data structure required for data communications at the presentation layer of OSI (Open System Interconnection).
2. Description of the Prior Art
A conventional protocol data generator-analyzer of this kind requires setting of or reference to values constituting PDUs in encoding or decoding of PDUs, which are transfer syntaxes used in data communications.
For example, to encode a PDU, the engineer has to understand complicated data structure of an abstract syntax described according to an international standard ISO 8824 Specification of ASN. 1 (Abstract Syntax Notation One) before manually creating a VTL (Value Tree List) for PDU encoding, which is a machine-processible list containing values corresponding to the data structure so as to set or refer to the values of the components.
On the other hand, for decoding of a PDU, the engineer has to manually check the abstract syntax against the VTL output from the protocol data generator-analyzer so as to pick up desired component values.
As described above, a conventional protocol data generator-analyzer requires manual operation for encoding and decoding of PDUs. Specifically, the engineer has to understand the data structure of PDU before creation of or reference to a corresponding VTL. It is quite troublesome to set desired values and refer to them. Besides, manual setting and reference may be accompanied by errors in setting or reference and omissions of data when the data structure is complicated. Further, plenty of time and labor is required for understanding of the data structure itself.